In a fuel cell power plant, a fuel gas such as hydrogen, is supplied to an anode of a fuel cell stack, an oxidant gas such as oxygen is supplied to a cathode, the fuel gas and oxidant gas cause an electrochemical reaction via an electrolyte membrane between the anode and cathode, and electrical energy is extracted. When the fuel cell stack and peripheral devices are housed in a casing, fuel gas which leaked from the fuel cell stack or peripheral devices may accumulate inside the casing, but it is not preferred from a safety viewpoint that inflammable fuel gas accumulates in the casing.
Tokkai Hei 8-31436 published by the Japanese Patent Office in 1996 discloses a ventilator for sweeping out gas from the inside of the casing. The ventilator comprises an electric fan for ventilation installed in the casing, an open/close type door, a sensor for detecting an inflammable gas concentration in the casing and a controller.
When the concentration of inflammable gas increases, the controller increases the fan rotation speed to increase the ventilation air volume.